This application is for funds to accomplish Specific aim 1: To determine whether or not histocompatible tumor resistance to P815 segregates with the H-2b histocompatibility allele in the backcross DBA/2 x B6D2F1; and specific aim 4: To generate congenic lines on a DBA/2 background selected by the criterion of histocompatible resistance to P815 based on survival.